Typical control methods for AC rotary electric machines obtain a value of each phase current flowing in an AC rotary electric machine. Then, the typical control methods send driving instructions to switching elements of an inverter for the respective phases of the AC rotary electric machine. This controls the switching elements to perform feedback control of a controlled variable accordingly; the controlled variable depends on the obtained value of each phase current. This feedback control results in an actual value of the controlled variable following a target value of the controlled variable.
Superimposition of harmonics, i.e. higher-order components, on at least one phase current flowing in an AC rotary electric machine during execution of such feedback control causes harmonics to be superimposed on the driving instructions for the respective switching elements of the inverter. This may result in harmonics being contained in, for example, switching noise of the inverter, resulting in greater noise.
Superimposition of harmonics on at least one phase current flowing in an AC rotary electric machine during execution of such feedback control also causes a problem of phase-current offset. The following describes the phase-current offset. Specifically, a reference level of 0 [A] for each phase current is learned based on a level of a corresponding phase current at the start-up of the AC rotary electric machine. However, the middle point of the peak-to-peak amplitude of at least one phase current is offset with respect to the reference level of 0 [A], which will be expressed as phase-current offset.
Phase-current offset occurring in at least one phase current may cause torque variations and/or power fluctuation of the AC rotary electric machine.
A known control apparatus for an AC rotary electric machine, which is disclosed in Japanese Patent Application Publication No. 2014-132815 to address the above problems, performs Fourier series expansion of measured values of, for example, first and second phase currents as a function of electrical rotational angle θ of a rotor of the AC rotary electric machine.
This Fourier series expansion calculates a pair of first-order Fourier coefficients for each of the first and second phase currents, and obtains, based on the pair of first-order Fourier coefficients for each of the first and second phase currents, a first-order component of a corresponding one of the first and second phase currents. Values of the first-order component of each of the first and second currents are a function of the electrical rotational angle θ of the rotor of the AC rotary electric machine.
Then, the known control apparatus performs, using the first-order component of each of the first and second phase currents, feedback control of the controlled variable to cause the actual value of the controlled variable to follow a target value of the controlled variable.
Specifically, the known control apparatus divides k period(s) of the electrical rotational angle θ of the rotor by N to obtain N integration angles where k is a positive integer variable equal to or larger than 1, and N is a positive integer variable. Then, the known control apparatus integrates values calculated based on values of the first phase current measured at the respective N integration angles over the k periods; the measured values of the first phase current are a function of the electrical rotational angle θ of the rotor. This calculates the pair of first-order Fourier coefficients for the first phase current.
Similarly, the known control apparatus integrates values calculated based on values of the second phase current measured at the respective N integration angles over the k periods; the measured values of the second phase current are a function of the electrical rotational angle θ of the rotor. This calculates the pair of first-order Fourier coefficients for the second phase current.